1. Field of the Invention
The present invention relates to cable shearing devices and, more particularly, to apparatus for cutting a cable or wire rope of the type utilized in concrete construction.
2. History of the Prior Art
The prior art is replete with concrete construction cable tensioning systems. These systems include both pre-stressed and post-tensioned cables and wire rope. Engineering in the post-tensioning of concrete is a well developed technology and the utilization of such tendons extending through a concrete slab or beam is conventional. The tendons provide structural strength for the concrete in a manner and at a cost not heretofore possible with conventional rebar construction. Utilization of such tendons does, however, require anchor assemblies on opposite ends thereof and the termination of the cable itself at the anchors. The anchor assembly secures the ends of the terminated tendons extending through the concrete bed whereby the tendons remain taut and effective during the life-span of the construction. The effectiveness requires the protection of the terminated tendons, which are usually made of steel or the like, from corrosion. Corrosive forces are well known to cause deterioration in the strength of the concrete if allowed to jeopardize the integrity of tensioning member. To prevent corrosion of the tendon, the steel fibers are usually sheathed in a plastic membrane throughout the length of the slab. The membranes do, however, require termination at the point where the tendons are secured within the anchor assemblies. The reason is obviously to provide appropriate structural integrity at the secured position.
In the process of post-tensioning, it is important that the tendon is free to move within the hardened concrete so that the tensile load on the tendon is evenly distributed along the entire length of the structure. Methods used to insure that the tendons provide free movement within the hardened concrete include laying a number of strands of wire in a sheath. It is within this sheath that the strands of wire are stressed after the concrete is hardened. After stressing, the wires exposed from the ends of the anchor assemblies are then cut-off or terminated. Just the opposite is true of pre-stressing concrete cables. With such cables, they are first stretched and exposed to the concrete during pouring. They are not covered with a protective sheath due to the fact that it is important that the concrete bond directly to the exposed, taut cable in its pre-stressed condition. Once the forms are set the tension in the cable is also established so that as the concrete cures it forms a bond directly to the cable and no cable movement is allowed without movement in the concrete itself. There are, of course, advantages to both systems depending on the type of fabrication utilized in the ultimate application.
The present invention pertains to terminating the tensioning cable at the anchor assemblies utilized in post-tensioning configurations. Pre-stressing configurations do not necessarily require such elaborate anchor assemblies and the associated termination problem because the cables are cemented in the concrete and can simply be out off during the form removal process. The present invention could, however, be useful in cutting such cable assemblies. Post-tensioning incorporates a duct or plastic tube as described above and the utilization of wedges or anchors on opposite ends to produce the tensile force transmitted through the mono or multi-strand cable. Since the force has to be applied after the concrete has cured up to a point, the tensioning must occur after pouring and the cable termination must occur subsequent thereto. Problems associated therewith are obviously the problem of terminating a cable that has been critically secured in a wedged configuration. The securement must not be effected during cutting and the cable must be left in a condition that does not jeopardize the integrity of the system. However, in many instances this "cutting" is completed by the utilization of a cutting torch, which, by definition, effects the cable, the wedges and the surrounding surfaces with intense heat.
A post-tensioned cable is not easily terminated. The cable is generally recessed within a pocket in the poured concrete and it is extremely difficult to obtain access to the cable with any cutting implement other than a cutting torch. The primary problem with cutting torches is the fact that the flame creates an intense heat that anneals the cable and the wedges which are used for locking the tensioned cable in place. Moreover, the degree of accuracy of a torch flame is limited. Annealing alone can very often cause ultimate failure of the tensioning system. In addition, the torch heat enhances the corrosive action of any moisture exposed to the terminated cables. It is well known that intense heat enhances corrosive forces and, as set forth above, it is critical that the cable be protected against corrosion. Most often, this is effected by enclosing the terminated cable or tendon, as it may be called, in a plastic coating or cup. Such a covering requires some exactitude in the cutting configuration so that a precise length is provided at the termination point. With torches and the like, the damage as well as the inaccuracies are manifest in many failures and costly mistakes.
The present invention provides an advantage over the prior art by providing a method of and apparatus for precise shearing of wire rope and cables in general, and post-tensioning cables in particular. The apparatus is designed to be matingly inserted into the recess or pocket of a post-tension formation area around the tendon. A precise cold shear of the cable is then effected. The cold shear cut is accomplished by the utilization of eccentric apertures in relatively small interlocking blocks which may be received directly within the formation pocket or recess. One block is generally cylindrical in shape and it is constructed with an aperture therethrough in an eccentric location therein. Another block is provided with an aperture formed centrally therethrough for receiving the cable to be terminated. Rotation of the cylindrical block relative to the other block thus produces shear forces that out the cable at a precise location without the damaging effects of heat and the like. In this manner the great advantage over prior art systems is afforded in an economically feasible configuration.